Discovering the secrets of manatee chat

By Natalija Lace

Did you know manatees chat to each other? And that they chirp like birds?

Not so long ago, Florida manatees (Trichechus manatus latirostris) were thought to be mostly silent, solitary herbivores with a simple communication system consisting mainly of contact calls between a mother and her calf.

However, research in recent years has suggested manatees might not be so solitary after all and may have a complex vocal repertoire that goes beyond simple parent/child communication.

When compared to other fully aquatic marine mammals like dolphins or whales, manatees’ vocal repertoire is limited, but we’re yet to fully understand the extent of their language, the degree of individual variations and, most importantly, the functions of their various calls.

Two manatee calls. We will be trying to determine if these are an exchange between two manatees or just one manatee calling out.

To address these gaps in our knowledge, Cetalingua Project (my research group which decodes marine mammal communication) has launched a citizen science study called “Manatee Chat” on the Zooniverse website.
First, we are asking people to help us identify manatees’ calls and eating noises by listening to sound files and visually examining a spectrogram (a visual representation of the sound and its frequency changes over time).
In the second phase, we will classify these sounds and decode the individual calls of specific animals.

Manatee Chat uses a very large dataset which I collected over several years at the Manatee Rehabilitation Center, Tampa Zoo at Lowry Park, Florida. The first thing many citizen scientists notice is how unexpectedly bird-like manatee calls are. Manatees are big: they can grow to over 4m (13ft) in length and weigh around 1400kg (220 stone) so it is surprising to hear their high-pitched chirps and squeaks. It is a mystery why they produce these sounds as lower frequencies would travel farther and allow them to keep in touch even over long distances.

Launched in March 2018, over 1200 citizen scientists have taken part in the project so far. They have already found a number of interesting and unexpected calls and even some mystery sounds that have not been identified yet.

An intense acoustic exchange between several manatees. What information, if any, is being communicated here?

Ultimately, the classifications made by volunteers will be used to produce better models to identify and classify all calls automatically. Such a system would have many conservational benefits and help to decode the functions of manatee calls.

This technology could help solve some of the mysteries that surround this enigmatic species such as how do they navigate? Can they remember and recognise fellow manatees they met years ago? What information do their calls convey? Do they have alarm calls? Why are they being hit by boats despite their excellent hearing?

We invite current and future citizen scientists to take a part in this project, not only because it contributes to scientific knowledge, but because it is interesting and fun. No two soundfiles are the same, and many of our current citizen scientists get excited when they find a clear call or an intense call exchange among several manatees. In the future, we plan to add video clips so citizen scientists can analyse behavioral states that correspond to the sound files and see elusive manatees up close.

A 2017 census found that only 6,620 manatees are left in Florida’s waters and even though the population has been recovering in recent years, manatees still face many challenges including boat strikes, cold stress (manatees cannot adapt to water temperatures below 20C and will experience metabolic slow-down, compromised immunity, and eventual death as they stop eating and lose weight), toxic algae blooms, and habitat destruction.
By learning more about these mysterious aquatic herbivores, we can better understand their ecology, biology, cognition, and communication.

Our Blue Planet is a collaboration between the BBC’s Natural History Unit and OceanX Media. Join the conversation on twitter; follow us @OurBluePlanet

Natalija Lace is a Founder and Principal investigator for Cetalingua Project. Lace received her PhD from the University of Southern Mississippi, USA and her main interests include form and function of marine mammal acoustic communication. You can read more about Natalija's research here.